Antenna with variable inductance for tuning



M. WEBSTER 2,839,752

ANTENNA WITH VARIABLE INDUcTANcE FOR TUNING June 17, 1958 Filed July 19, 1954 IN1/EN TOR. Maw/v M5557?? United States Patent O ANTENNA WITH VARIABLE INDUCTANCE FOR TUNING Marvin Webster, Mill Valley, Calif.

Application July 19, 1954, Serial No. 444,050

12 Claims. (Cl. 343-745) This invention relates broadly to variable inductance elements and to an inductance ot the variable type particularly suited to use as a central loading element oi a mobile antenna usable on wide range frequencies.

In its particular application the variable inductance element will be herein described with respect to its relationship to an adjustable and stationary component together comprising an antenna, but it is to understood that the invention also may provide the inductance element for other forms of installations, as, for instaucV the loading coils on transmission lines and the like.

Various forms of the so-called whip type of antenna are known. These nd particular use in connection with vehicular radio equipment of many types and sorts although one of their most important t es is in connection with transmitting equipment. with automobile installations, a socalled whip-type of antenna is generally the only suitable form to he em ployed. This is because of the danger of the antenna striking obstacles which cause it to bend, and, also be cause of the fact that the installation is frequently subject to violent vibrational effects which fatigue the metal of which the component is formed and frequently render the antenna liable to breakage under stress.

The antenna incorporates features of the sort which make it ideally adapted to the mentioned uses be in addition, the antenna herein to be described is of such form as to provide an over-all weatherproof construction through the thorough and complete protection of all of its metallic parts. In addition, the antenna herein to be described is of a type which, in its construction, is light in weight, suiiiciently flexible to take up shock and yet suiciently rigid to prevent excessive sway at high vehicle speeds and adaptable for use over a wide frequency range.

In its preferred construction the inductive element by which tuning of the antenna is brought about constitutes the central loading element of the antenna. it is secured at one end to a moderately rigid and yet ilexible column in which the main or lower antenna segment or part is held and which column may be rigidly fastened at one end to the vehicle upon which it is to be carried. The inductive element is preferably wound upon a tubular support core which may, if desired, be an extension of the same tubular core in which the main antenna section is housed. Protruding from the end of the tubular meniber upon which the inductive element is wound and which, if surrounding the main section, is remote therefrom there is supported in an adjustable fashion a top or upper antenna section of generally whip-like characteristics capable of being slidably mounted with respect to the tubular core and adjustable to Various positions longitudinally of the tubular member and internally thereof. Provision is made for securing the upper or outer antenna section in various positions of penetration into the core. By Way of a suitable circular coupling or contacting component attached to one end of the upper or outer antenna section and positioned internally of the tubular member and of the winding thereon there is provided a series circuit between the main antenna section and the upper or outer antenna section through the wound conductor. The tapped portion of the winding serves as an inductive or loading element between the two end conductors or an- Particularlv in connection 2,839,752 Patented June 17, 1958 Mice tenna sections. The portion of the inductance tapped is selectable. Therefore the frequency to which the antenna combination may be tuned is established by the relative adjustment of the upper or outer conductor or antenna section with respect to the tubular member as determined by the point on the wound conductor through which the series circuit is established.

Further than this, the circular coupling or contacting component of the sort preferably adopted is one formed by looping or winding helically a conductor into a multiplicity of turns and then looping the so-wound conductor until the ends thereof are in substantial Contact so that the looped component forms a substantially toroidalshaped element which may be held in such form by suitable abutting anchoring or positioning means supported at either side thereof.

In its use, the coupling or contacting element in its toroidal form is so arranged that the toroid axis is parallel to or even coincident with the axis of the tubular member within which it is positioned. Thus, the turns of the toroid are so arranged that the outer toroidal periphery substantially contacts the inner wall of the tubular member and the complete toroid occupies a position substantially transverse or cross-section-wise of the tubular element.

To establish the inductive value of the conductor wound upon the tubular element which shall be included in the electrical path between the inner and outer conductors the wound conductor which is to form the inductance is preferably located for a portion of each turn in slots or notches formed, for instance, by cutting into the wall of the tubular element and wrapping the wire so that each wire turn rests in one of the notches, grooves or slots. Where there is to be direct contact established between the circular coupling or contacting means and the wound conductor such connection is established internally of the tubular member and by providing the slot or notch to extend completely through the wall the wound conductor when spanning the notch or slot extends inwardly from the circular periphery to a very slight extent so as to form the chord of an arc measured by the arcuate distance over which the slot is cut. The circular coupling or contacting component when located internally of the tubular member serves to contact the turns of the conductor wound and held in supported position by the notches. Changed longitudinal positions of the coupling element include more or less turns between it and the connected main conductor. The number of turns wound upon the tubular member, of course, should be sufficient to permit resonance to occur at the lowest frequency in the band over which it is to be used.

With these structural features in mind there are accord-- ingly included among the objectives of the invention those of providing an inductance of a variable type adapted for general use, although particularly adapted to antenna 'nstallations; also to provide an antenna installation which will incorporate mechanical strength, flexibility, light weight, a high degree of protection against weather and a component which can readily be precalibrated so that the user, by extending the upper or outer antenna conductor relative to the main tubular support, may determine readily the resonant condition at which the antenna is to operate. Other and further objects of the invention will become apparent from a consideration of the follow ing description and appended claims in connection with the accompanying drawing wherein:

Fig. 1 is a schematic illustration of one preferred form of the invention;

Fig. 2 is a broken section through a portion of Ythe upper part of Fig. l;

Fig. 3 is a sectional view taken on the line 3-3 of Fig. 2; and

Fig. 4 is a view to illustrate the use of the notches on the tubular member to locate the wires of the wrapped conductor, as shown also in section by Fig. 2, and the establishment of coupling or contact between the wrapped conductor and the slidable element.

Referring now to the drawings for a further understanding of the invention the lower section 11, as shown by Fig. 1, discloses a tubular sheath or outer covering which is preferably formed of glass liber cloth impregnated with a thermosetting plastic. longitudinally positioned within this sheath is a central conductor of smaller diameter which may, for instance, be a conductor of the sort disclosed in applicants United States Letters Patent No. 2,681,412, granted June l5, 1954, which conductor may be fitted quite closely within the internal diameter` of the sheath or which Ymay be imbedded within the sheath by a filling of plastic which is also of the thermosetting variety. The lower end of the antenna installation and the tubular element 1 fits into a deep collar 13 which has an inside diameter adequate to accommodate the butt end of the tubular sheath 11, which may be secured or cemented therein by an appropriate adhesive suitable for use with a plastic used for the impregnation of the glass fiber cloth, such as Bakelite cement. This fitting preferably terminates in a threaded stub which may be used to support the complete assembly in any suitable litting. The internal conductor 17 forming the main or lov er antenna conductor element is electrically connected to this fitting in any desired way, such as soldering or brazing in a central hole in the stub end of the fitting.

The tubular member 11 in the illustration shown extends from the collar 13 upwardly to join to an upper closely fitting collar 19 which is threaded at its upper and outer end 21 for the attachment thereto of one end of a mounting flange and ring 23. The portion of the tubu lar member 11 which extends beyond the termination of the internally positioned main or base antenna section 17 is to support a multiplicity of turns of a wound conductor 25 which is wrapped thereabout throughout substantially the remainder of the length of the tubular sheath. The tubular sheath has a series of notches or slots 27 cut into its periphery at regularly spaced distances from each other. These slots or notches extend substantially parallel to each other and are, in the preferred form, cut so as to extend completely through the wall of the tubular sheath to such an extent that when the conductor 25 is wrapped about the outer portion of the tubular sheath 11 it will, when overlying the notches or slots, form itself into substantially the chord of an arc, as particularly shown at 29 in Fig. 3.

The remainder of the conductor is wrapped about the outer periphery of the tubular sheath 11 but that portion of the conductor forming the chord of the arc as shown at 29 penetrates within the inner circular boundary of the sheath. The conductor forming the chord 29 of the arc is preferably stripped of insulation over that distance which it occupies within the notch or slot for reasons which will later become apparent. If desired, and for reasons that will be explained at a later point, the complete conductor may be wrapped without insulation, it being appreciated, of course, that the tubular sheath 11 formed of glass ber cloth is of itself an insulator preventing the short circuiting of the conductor turns in the wrapping. The slots or notches thus form a series spaced along the tubular sheath extending generally from approximately one end thereof (see Fig. 2, for instance) longitudinally to the plane of termination of the internal conductor 17. The wrapped wire 25, as located by the notches 27, is then secured to the sheath and appropriately formed into electrical contact with the main conductor forming the lower part of the antenna by a suitable'connector or by -the illustratively indicated soldered joint 31 (see Fig. 4), The opposite end of the conductor is suitably secured and anchored to the sheath 11 in any desired manner (not shown) at a point closely adjacent to the region of attachment of the threaded collar 19. The notches or slots 27 are preferably, although hot necessarily, in generally circularly staggered arrangement with respect to each other so that adjacent slots or notches are located at different angular positions relative to the tubular element. This causes the notches or slots to -form generally according to a helical pattern with respect to the length of the tubular member, with the pitch of the so-formed helix measured (..ong the tube axis. Likewise, the turns of the conductor wound between the point of attachment 31 to the main conductor or base antenna section and the upper end of the tubular member 11 forms the wrapped wire into substantially 'helical form. Various numbers of turns may be provided depending of course upon the wave length upon which the antenna unit is to be used,

assuming of course that the inductance formed by the wrapped conductor shall be usable from substantially its outer end through to its connection to the internal member.

As an alternative to providing the main or base an- 'Y tenna section within the sheath 11 in the form described and as shown in United States Letters Patent No. i

on the surface where the notches or slots 27 happen to be l formed. Since for constructional reasons and for cheapness of Vmanufacture it is frequently desirable to wrap the conductor 25' in the form of an uncoated wire, it is frequently desirable to wrap outer insulating coating thereabout. The outer insulating coating wrapped about the wound conductor serves a dual purpose of enclosing the wrapped wire and protecting the arrangement internally from weather effects, dampness and the like, and it Valso provides that portion of the wrapped lconductor which is about the periphery of the tubular member 11 v with an insulating covering.

The coupling or Contact to the individual turns of the wrapped conductor is provided on that portion which extends internally of the tubular member and along the various chords 27. This coupling or Contact servesv to establish an electrical circuit between their outer or upper antenna conductor 35 and the main or inner conductor 17 so that there are two conductors separated from each other by the wrapped conductor forming the loading inductance. Since the illustrated antenna combination is to be tuned to resonance at diierent selected `frequencies it will be appriated that the amount of inductance included between the inner or main conductor 17 and the outer conductor 35 must be varied to make the antenna of maximum efficiency at various wavelengths. To this end the upper or outer conductor is supported from one end of the tubular member by a suitable weatherproof packing gland y38 which extends outwardly from the mounting flange and ring 23. The upper or outer conductor is supported within the packing gland 33 so as to be longitudinally movable in and out of the tubular member 11. In most instances it is desirable that the upper or outer conductor 35 be covered with a protective sheathing or insulating covering 37 to protect the component from the weather and to provide both resilience and general reinforcement.

In the general form herein depicted the upper conduc-tor 35 is positioned within a exible fiber glass {sheathing which, illustratively, may be o-f the general form shown in United States Letters Patent No. 2,681,412 hereinabove mentioned. Alternatively, the upper conductor may be covered with other forms of insulating material or sheathing or it may even be bare but it is esirable or possible to provide the covering in order to insure greater resilience, greater strength, and the like.

The so-covered outer or upper conductor 35 is then caused to be supported within the packing gland 38 as above stated, and is movable through the packing material 39. Suitable washers or O-rings 41 are usually desirable for providing a tight tit and for the purpose of clamping the assembly. An upper or outer nut 43 is attached to the end of the sleeve 38 to hold it together. The complete sleeve is secured to the threaded end 21 of the collar i9.

With the arrangement thus provided the end of the outer or upper antenna conductor 35 which tits within the tubular member 11 has secured to it the circular coupling or contactor which is shown more particularly by Figs. 2 and 3. The coupling or contactor, as a whole, is preferably in the form of an elongated conductor 49 which is helically wrapped and bent back upon itself in such a fashion that the winding at one end is preferably formed slightly tighter and on a lesser radius than the remainder of the winding so as to form a terminating end 51 which, when looped, will t within the opposite terminating end 53. The so-looped helically wrapped conductor then forms, when its ends are caused to meet, a f

toroidal shaped wrapped winding which is more particularly evident from the showing in Fig. 2 where the toroid is depicted at 55.

The outer diameter of the toroid so formed lis approximately that of the inner diameter of the tubular member 1l. The inner toroidal diameter is slightly less than that of the recessed portion 57 of a sleeve 59 into which the inner end 61 of the wrapped upper or outer conductor 35 is caused to tit and through which there is preferably provided a central opening 63 at the inner end. The recessed portion 57 provides a shoulder where it meets the sleeve 59. A washer or ring 65 rests against the sleeve and the wrapped conductor formed into the toroidal configuration is caused to abut the washer. The opposite surface of the so-formed toroidal conductor is then caused to rest against a second ring or ilange-like member 67. This ring either is spaced from ring 65 by a collar 6% which surrounds the recessed sleeve portion 57 and against which the inner surface of the toroid 55 v may rest or the collar may be formed directly on one of the washers. The outer portion of the recessed sleeve 57 is preferably threaded, as shown at 71, and the combination of the two washers or rings 65 and 67, as well as the collar 69, is held closely together by the tightening nut 73.

It is important to note at this point that the outer diameter of the washers or rings 65 and 67 is slightly less than that of the outer diameter of the formed toroid 55 but of greater diameter than the inner diameter of the soformed toroid. In this way the washers or rings maintain the toroid permanently in place when the ends of the conductor are looped back upon themselves and yet the individual turns of the toroid extend beyond the rings or washers 65 and 67 so as to make contact with the wrapped conductor in the region where it extends within the inner periphery of the tubular member 11 substantially along the chord 29.

The outer or upper antenna conductor 35 is electrically connected through the sleeve 59, which is formed of conducting material into which it is preferably force fitted, through to the conducting rings or washers 65 and 67 and to the turns of the toroid 55 so that when the toroidal member contacts the wrapped conductor 25, which connects to the inner or main conductor 17, an electrical path is formed between the outer or upper conductor and the lower or main conductor through a portion of the inductance element 25. The contact with the wrapped conductor 25 is substantially in the form shown in cross section by Figs. 2 and 3, Fig. 2 particularly showing the longitudinal relationship along the tubular member 11 and the wrapped conductor thereon and Fig. 3 showing that a plurality of the turns of the wrapped conductor forming the toroid contact the conductor 25. lt will be observed that the toroidal shape is slightiy distorted from a true circular pattern at its periphery in the range where the conductor 25' is contacted. along the chord 29, as is shown particularly by Fig. 3.

The toroidal arrangement of the contactor or coupler 55 provides for contacting the conductor 25 which penetrates within the inner periphery of the tubular member 1l regardless of the staggered position of the slots or notches cut thereon. Also, regardless of the relative angular rotation of the outer and inner conductors 35 and 17, the Contact is established.

It was above mentioned that the conductor 25 wrapped about the periphery of the tubular member 11 is preferably coated or covered with a suitable insulator or covering which is particularly shown by the covering generally designated in schematic form at 77. This covering is preferably in the nature of a bonded or highly flexible ber glass jacket to provide complete protection against the weather.

In Fig. l the capacity to ground of the top whip section is schematically illustrated by the dotted condenser 79. The combination, when used as an antenna, offers the advantages of a resonant centrally loaded component. The capacity to ground of the top section and the inductance of the loading section are such that the maximum current loop occurs near the center of the antenna rather than at the base or at the connecting leads. The normal base impedance of an antenna of the character herein described is generally very low or of the order of 7 to l5 ohms, the exact values, of course, being dependent upon the positioning of the antenna and the length of the connecting lead (not shown) from the base mount to the radio equipment used therewith.

The construction herein described is such that merely by raising or lowering the upper or top section of the antenna, considering the upper or outer conductor to be the movable section, will provide for establishing an electrical circuit between the lower or main end and the upper end through the internally exposed loading coil turns. By raising or lowering the outer or upper section so as to move the circular contacter internally of the wrapped e conductor 25 more or less turns of the wrapped conductor may be tapped. There is thus provided an arrangement by which the obtainment of any continuous adjustment of the loading inductor to provide antenna resonance at any selected wavelength within a band may be realized. It minimizes loading problems and improves the over-all efficiency. Clean contacts between the turns of the toroid 55 and the contacted winding sections of the wrapped conductor 25 are assured by reason of the slidable form of contact obtained, which makes the contacts essentially self-cleaned.

It will be appreciated, of course, that various modifications of the arrangement herein described may be had and used without departing from the spirit and scope of the invention included among which may be, for instance, the provision of a main or lower antenna section which is completely free of the tubular member upon which the wrapped conductor 2S is supported with appropriate contact and connection made between the wrapped conductor and the main antenna section. ln this way the main antenna section may serve as one conductor of any sort which is to be linked to another conductor, such as the outer or upper conductor 35, through a selected inductance which may be varied.

Other modications, of course, will become apparent and suggest themselves to those skilled in the art in the light of the description of the mechanism herein set forth.

Having now described the invention, what is claimed is:

l. A variable inductance comprising a tubular member of insulating material having a longitudinal series of substantially parallel slots, generally regularly spaced and transverse tothe tube axis, cut through the wall thereof, a. conductor anchored to the tubular member substantially adjacent to one end slot of the series and wrapped around said tubular member so that each conductor turn rests in one of the slots and the conductor is generally helically wound about the periphery of the tubular member, said wrapped conductor being free from insulating covering in the region of its Contact with the cut slots, said wrapped conductor also being anchored to the tubular member at a point generally adjacent to the slot forming the other end of the series, a connector establishing electrical connection from one anchored end of the wrapped conductor to a tlrst main conductor, a sec ond main conductor supported from the tubular member at the end opposite that at which the connecter is secured to the wrapped conductor, and adapted to extend internally of the tubular member for at least a portion of its length and to be adjustable longitudinally internally thereof, a circular coupling means connecting to the second main conductor and secured at the end thereof positioned within the tubular member, said circular coupling means compri-sing an helically wound conductor looped into substantially circular configuration so that its ends are in substantial contact and the looped coniiguration forms the circularly wound conductor into a generally toroidal formation v/ith the toroid axis substantially parallel to the axis of the tubular member, means to secure the looped conductor in the toroidal form, and means to support the second main conductor and the circular coupling means in longitudinally adjustable positions within the tubular member relative to the conductor wound thereon to determine the number of turns oi` the conductor wound upon the tubular member included between the contacter and the connector as determined by the longitudinal penetration ofthe circular coupling means within the tubular member.

2. The combination claimed in claim l wherein the slots are cut into the tubular member in substantially parallel and regularly spaced relationship are formed at different peripheral arcs in the tubular member from one end of the tubular member toward the other so that the slots appear in an helical arrangement with the spiral pitch measured along the axis of the tubular member.

3. An antenna compn'sing a tubular member of insu lating material having a longitudinal series of substantially parallel slots, generally regularly spaced and transverse to the tube axis, cut through the wall thereof, a conductor anchored to the tubular member substantially adjacent to one end slot and wrapped around said tubular member so that each conductor turn rests in one of the elo slots and the conductor is generally helically wound about Y the periphery of the tubular member to constitute a loading inductance, said conductor also being anchored to the tubular member at a point generally adjacent to the slot forming the other end of the series, a main antenna conductor adapted for electrical connection to one anchored end of the wrapped conductor, an out-er antenna conductor supported from the tubular member at the end opposite that at which the main antenna conductor is adapted to connect to the wrapped conductor sc as to extend internally of the tubular member for a portion of its length and to be adjustable longitudinally internally thereof, a circular coupling means electrically connected to the outer antenna conductor and secured at the end thereof positioned within the tubular member, said circular coupling means comprising an helically wound conductor looped into substantially circular conliguration so that its ends are in substantial contact and the looped conguration forms the circularly wound conf ductor into a generally toroidal formation with the toroid axis substantially parallel to the axis of the tubular member, means to secure the looped conductor in the toroidal form and means to support the outer antenna conductor and Ythe circular coupling means in longitudinally adjustable positions relative to the conductor wound Vupon the tubular member to establish a series circuit between the main antenna conductor and the outer antenna conductor through a portion of the conductor wound upon the tubular member determined by the longitudinal penetration of the circular coupling means within the tubular member.

4. The combination claimed in claim 3 wherein the slots are cut into the tubular member in substantially parallel and regularly spaced relationship are formed at different peripheral arcs on the tubular member from one end of the tubular member toward the other so that the slots appear in an helical arrangement with the spiral pitch measured along the axis of the tubular member.

5. A center loaded antenna comprising a base antenna conductor, a tubular support column surrounding said conductor and extending beyond the length thereof, a series of substantially parallel spaced notches formed into the wall of the tubular support column in the region beyond the end of the internally positioned base conductor, said notches extending in planes generally trans- `.'erse to the axis of the tubular column, an inductance comprising a helically wrapped conductor formed into the end section of said support column extending beyond the base conductor with each notch serving as a locator and spacer for each conductor turn, an electrical connection between the end of the conductor within the support column nearest the wrapped conductor and the said wrapped conductor, an upper antenna conductor, a circular contacter secured to one end of the upper antenna conductor, means to support the upper conductor and the circular contactor within the tubular support column for slidable longitudinal movement therein, and means provided by the circular contacter for establishing electrical connection between the upper conductor and the inductance independently of the position of relative angular rotation between the base and upper antenna conductors so as to provide a series connector between the two said conductors through the inductance with the portion of the inductance between the slidable contactor and the connection to the base conductor serving to tune the antenna combination to resonance at a frequency dependent upon the value of inductance included between the antenna conductors.

6. The combination claimed in claim 5 wherein the parallel and spaced notches are cut into the tubular member in substantially a spiral whose pitch is measured along the axis of the tubular member.

7. The antennaclaimed in claim 6 comprising, in addition, a packing gland closing the wrapped end of the tubular member and supporting the upper antenna conductor for slidable positioning'longitudinally adjustable within the tubular member and means for clamping rigidly the upper conductor at selected points relative to the positioning within the tubular member.

8. The antenna claimed in claim 7 comprising, in addition, a support mounting at the end of the tubular member from which the base antenna conductor is supported to establish electrical connection to said conductor.

9. An antenna comprising a tubular member of insulating material having a series of substantially parallel slots, generally regularly spaced and extending transverse to the tube axis, cut into the periphery thereof and eX- tending along the length ot the tubular member, a conductor secured at one end to the tubular member substantially adjacent to one end slot of the series and wrapped around said tubular member so that each condoctor turn rests in one of the spaced slots and the conductor Ais generally hclically wound along the periphery of the tubular member to constitute a loading inductance, said conductor terminating substantially adjacent to the opposite end slot of the series and secured to the tubular conductor, a main antenna conductor adapted to make electrical connection with the end of the wrapped conductor,' at substantially end slot' of the series, an upper antenna conductor supported from the conductor wrapped tubular member at its end nearest the other end slot of the series and adapted to extend internally of the tubular member and to be adjustable longitudinally internally thereof, a circular contacter electrically connected to the outer antenna conductor secured at the end thereof positioned wi in the tubular member, said circular contactor comprising an helically Wound conductor looped into substantially circular configuration so that its ends are in substantial contact and the looped configuration forms the wound conductor into a generally toroidal formation ot' which the axis is substantially parallel to that of the tubular member, means to secure the looped conductor in the toroidal form, and means to support the outer antenna conductor and the circular contactor in electrical connection with the conductor wound upon the tubular member so that the outer antenna conductor is maintained a series circuit with the main antenna conductor through that portion of the inductance formed by the conductor wound upon the tubular member determined by the inwardly penetration ot' the outer conductor and the circular con'tactor into the tubular member.

10. A centrally loaded antenna comprising, in combination, an outer conductor, a tubular member, means to support the outer conductor from one end of the tubular member so that said outer conductor may be moved longitudinally inwardly and outwardly internally of the said tubular member, a series of parallel notches formed in substantially uniformly spaced relationship within the wall of the tubular member and extending in planes transverse to the axis of the tubular member and each extending to a depth greater than the thickness of the wall of the tubular member, a conductor secured at each of its ends to the tubular member and wrapped so that the remainder extends about the outer periphery of the tubular member with individual turns located in the notches and spaced from one another by a distance determined by the notch spacing, said wrapped conductor being `bare of insulation in the region within which it rests in the notches, a main antenna conductor adapted to electrical connection with one end of the wrapped conductor, a circular contacter electrically connected to the end of the outer conductor supported for longitudinal movement within the tubular member, said circular contactor comprising an electrically wound conductor looped with its ends in substantial contact and forming substantially a toroid whose axis is parallel to `the axis of the tubular member and whose outer periphery contacts the conductor wrapped around the tubular member in the region coinciding with the notch cut into the tubular member and means for adjusting the position of the outer antenna conductor and the thereto attached circular contactor internally of the tubular member so that the outer and main antenna conductors are serially connected with each other through a portion of the turns of the wrapped conductor providing an inductance of adjustable magnitude determined by the position of the contactor and its spacing from the end of the wrapped conductor secured to the main antenna conductor.

11. A centrally loaded antenna comprising, in combination, an outer conductor, a tubular member, means to support the outer conductor from one end of the tubular member so that said outer conductor may be moved longitudinally inwardly and outwardly internally of the said tubular member, a series of parallel notches formed in substantially uniformly spaced relationship within the wall of the tubular member and cxtending in planes transverse to the axis of the tubular member and each extending to a depth greater than the thickness of the wall of the tubular member, a conductor secured at each of its ends to the tubular member and Wrapped so that the remainder extends about the outer periphery of the tubular member with individual turns located in the notches and spaced from one another by a distance determined by the notch spacing, said wrapped conductor being bare of insulation in the region within which it rests in the notches, a main antenna conductor adapted to electrical connection with one end of the wrapped conductor, an insulating wrapping covering the said tubular member at least throughout that portion of its length surrounded by the wrapped conductor for insulating the wrapped conductor for external Contact circular contactor electrically connected to the end or the outer conductor supported for longitudinal movement within the tubular member, said circular contacter comprising an elect. .lly wound conductor looped with its ends in substantial contact and forming substantially a toroid whose axis is parallel to the axis of thc tubular member and whose outer pc-riehery contacts the conductor wrapped aro: d the tubular member in the region co- Witt n., notch cut into the tubular member and me ns for adjusting the position of the outer antenna conductor and the thereto attached circular contacter internally of the tubular member so that the outer and main antenna conductors are serially connected with each other through a portion of the turns ot the wrapped conductor providing an inductance of adjustable magnitude determined by the position of the contacto-r and its spacing from the end of the wrapped conductor secured to the main antenna conductor.

l2. An antenna comprising a tubular member of insulating material having a longitudinal series of substantially parallel slots, generally regularly spaced and transverse to the tube axis, cut through the wall thereof, a conductor anchored to the tubular member substantially adjacent to one end slot and wrapped around said tubular member so that each conductor turn rests in one of the` slots and the conductor is generally helically wound about the periphery of the tubular member to constitute a loading inductance, said conductor also being anchored to the tubular member at a point generally adjacent the slot forming the other end of the series, a main antenna conductor connected to one anchored end of the wrapped conductor, an outer antenna conductor supported from the tubular member at the end opposite that at which the main antenna conductor contacts the wrapped conductor so as to extend internally ot' the tubular member for a portion of its length and to be adjustable longitudinally internally thereof, a circular coupling means in electrically conductive relationship to the outer antenna conductor and secured at the end thereof positioned within the tubular member, said circular coupling means comprising an helically wound conductor looped into substantially circular configuration so that its ends are in substantial contact and the looped configuration forms the electrically wound conductor into a vgenerally toroidal formation with the toroid axis substantially parallel to the axis of the tubular member, means to secure the looped conductor in the toroidal form and means to support the outer antenna conductor and the circular coupling means in longitudinally adjustable positions relative to the conductor wound upon the tubular member to establish a series circuit between the main antenna conductor and the outer antenna conductor through a portion of the conductor wound upon the tubular member determined by the longitudinal penetration of the circular coupling means within the tubular member.

References Cited in the le of this patent UNITED STATES PATENTS 739,176 Heal -Sept. 15, 1903 1,768,666 Conrad July 1, 1930 2,070,376 Sherwood Feb. 9, 1937 2,523,896 Bartolmei Sept. 26, 1950 2,719,920 Ellis Oct. 4, 1955 FOREIGN PATENTS 366,150 Great Britain Feb. 4, 1932 645,898 Great Britain Nov. 8, 1950 

